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With atomic clock at CU-Boulder, NIST sets new precision records

By Charlie Brennan, Staff Writer

Posted:
04/21/2015 09:30:49 AM MDT

Updated:
04/21/2015 10:49:34 PM MDT

JILA's strontium lattice atomic clock now performs better than ever because scientists literally take the temperature of the atoms' environment. Two specialized thermometers, calibrated by NIST researchers and visible in the center of the photo, are inserted into the vacuum chamber containing a cloud of ultracold strontium atoms confined by lasers. (Courtesy photo)

The National Institute of Standards and Technology in Boulder announced today that the latest modification of a record-setting strontium atomic clock has achieved precision and stability levels that now mean the clock would not gain or lose one second in about 15 billion years — approximately the age of the universe.

As reported Tuesday in Nature Communications, the experimental strontium lattice clock at JILA, a joint institute of NIST and the University of Colorado, now is more than three times as accurate as it was last year when it set a previous world record for precision.

Researchers don't believe they have approached the boundaries of what is possible.

"This excites us a lot," said JILA/NIST fellow Jun Ye. "I don't see the current results as limiting, at all. I see myriad possibilities opening up, allowing us to achieve greater precision down the road in the next decade."

Precision, in this context, refers to how closely the clock approaches the true resonant frequency at which the strontium atoms oscillate between two electronic energy levels, according to a news release.

Precision timekeeping has a wide array of potential applications, including positioning technologies such as global positioning systems, improved communications systems and more. Other uses could include a sensitive altimeter utilizing changes in gravity, or experiments that probe quantum correlations between atoms.

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The JILA/NIST clock holds a few thousand strontium atoms in a 30-by-30-micrometer column of roughly 400 pancake-shaped regions which are formed by intense laser light known as an optical lattice.

Scientists record strontium's ticks, which come at about 430 trillion per second, by bathing atoms in a stable laser light at the exact frequency that triggers the switch between energy levels.

With better lasers, and using those lasers on a far larger number of atoms, much greater advances in measurement science can be made, Ye said.

Through the work of Ye and his colleagues, including researchers at NIST's headquarters in Maryland, the clock's stability — gauged by how closely each tick matches every other tick — has also been bettered by nearly 50 percent, which is another world record.

Now, the JILA clock is good enough to measure very slight changes in the passage of time and the force of gravity at different heights. In his theory of relativity, Albert Einstein predicted that clocks tick faster at higher elevations.

"Our performance means that we can measure the gravitational shift when you raise the clock just 2 centimeters on the earth's surface," Ye stated in a news release. "I think we are getting really close to being useful for relativistic geodesy."

Relativistic geodesy is the use of a network of clocks as gravity sensors to make 3D precision measurements of the shape of the Earth. Ye is in agreement with other experts who have concluded that when clocks can sense a gravitational shift at 1 centimeter differences in height, slightly better than they currently perform, they could be used to achieve more frequent geodetic updates than possible using conventional technologies.

Putting a much finer measurement to critical changes to the Earth, such as rising oceans or melting glaciers, could also be facilitated through such science.

"I'm not being immodest. This gives us a lot of optimism for future growth in this area," Ye said. "I am very excited by the future prospects, as we continue to push this precision boundary."

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